Normal function of the Rb/E2F tumor suppressor pathway is compromised in all human tumors. Therefore, its function and regulation are areas of critical importance and intense interest for cancer research. pRb controls the cell cycle transition from G1- to S-phase through its repression of the E2F transcription factors. The Rb/E2F pathway regulates a diverse set of activities, and an investigation into the functional components that comprise the pathway would provide valuable insight into the biology of cancer. To obtain a deeper understanding of the Rb/E2F pathway, I propose to decompose the pathway into its constituent functional components using a computational approach, and then to investigate the associations among the functions, regulatory mechanisms, and clinical significance of the pathway components. In addition, I will also elucidate the functional relationships between the intertwined Rb/E2F and p53 pathways, yielding novel insight into the complex interactions between these tumor suppressor pathways. To investigate these issues, I will leverage methods I previously developed to decompose pathways and to infer the transcriptional regulatory proteins that drive their expression. Thus, the goals of this proposal are: (1) to decompose the Rb/E2F pathway into a series of independently functional pathway components regulated by identifiable transcriptional regulatory proteins, (2) to evaluate the correspondence between the components of the Rb/E2F pathway and identified regulators of the cell cycle, and (3) to identify components that connect the intertwined Rb/E2F (cell cycle initiation) and p53 (apoptosis) pathways. These studies would lead to the development of novel methodologies that provide the opportunity to obtain a deeper understanding of the precise components that effect pathway functions, and elucidate the functional connections among the interrelated pathways in a general cellular context, a goal of systems biology. Ultimately, the ability to characterize and measure individual facets of pathway activity will facilitate the development of ever more finely tuned personalized therapeutics. RELEVANCE TO PUBLIC HEALTH Rb is a tumor suppressor that is dysfunctional in all cancers, leading to a cascade of various poorly understood activities brought about by the E2F proteins. I propose to develop computational methods to identify these activities and study them individually, instead of as a whole. I believe that this will lead to a deeper understanding of the function of this pathway, as well as the drugs that target it.